Modelagem da qualidade da água da bacia hidrográfica do rio Paraibuna na área urbana do município de Juiz de Fora/MG: cenário atual e futuro

Abstract

In order to guide and substantiate the execution of the provisions contained in Brazil’s National Water Resource Policy, Law 9,433 of 1997, as well as the new legal framework for basic sanitation, Law 14,026 of 2020, which guide the planning, monitoring and management of hydrographic basins, the present work aimed to contribute to the building of information structures about the Paraibuna River and its hydrographic basin, especially those related to the quantity and quality of its waters. The river section under research encompasses the central and most urbanized region of Juiz de Fora, in the state of Minas Gerais, which totals an extension of 22.3 km within scope. The field campaigns took place in September/2019 (dry season) and March/2020 (rainy season). For the assessment of water quality, samples were collected superficially (20 to 30 cm deep) and analyzed in situ as for: dissolved oxygen (DO), temperature, pH and electrical conductivity by means of a multiparameter probe. The BOD was analyzed in the laboratory. The flows in the Paraibuna River were measured upstream of each outlet of six tributaries. Data on average speed, depth of the river, roughness coefficient, distance covered and width of the river were also collected. Environmental data on temperature, relative humidity and rainfall on the collection day were obtained from a weather station. For the simulation of current and future water quality scenarios in the evaluated section of the Paraibuna River, QUAL2K software was used. Data on water quality with poor quality were found, and we reach the conclusion that the flow has a direct influence on water quality. The flow of the Paraibuna River upstream and downstream of the section under study during the dry and the rainy seasons was 3.92 and 7.02 m3 s-1, and 60.25 and 66.44 m3 s-1, respectively. During the dry season, an OD of 0.67-1 mg L was found in the Paraibuna River and a BOD of 138 mg L-1 was found in the Matirumbide tributary. When calibrating the QUAL2K mathematical model for the section of the Paraibuna River, we conclude that the values that best fit the deoxygenation coefficient (K1) ranged from 0.01 to 2.95 d-1, and the reaction coefficient (K2) ranged from 0.70 to 3.15 d-1. As for the simulated scenarios, we reached the conclusion that the best result obtained for the sewage treatment of the Paraibuna River will be achieved when the conditions of scenario 3 are applied. This scenario includes the Wastewater Treatment Plants of União Indústria, Santa Luzia and the renovation of the Wastewater Treatment Plant of Barbosa Laje, with an expected reduction of 90% of the polluting load in the streams covered by the present work and a reduction of 50% of the organic load upstream of the section under study.